1. Field of the Invention
The present invention relates to an image forming apparatus including a rotatable belt member which is stretched over a plurality of rollers.
2. Description of the Related Art
In the related art, an electrophotographic type image forming apparatus is known. In such an image forming apparatus, a primary charging device uniformly charges a surface of an image bearing member, and then an exposing device irradiates the image bearing member with light to form an electrostatic image on the surface of the image bearing member. Then, toner of a developer (including carrier and toner, or including toner) is developed from a developer bearing member arranged in a developing device to the image bearing member. The developed toner is transferred to a recording material by a transfer device, and the recording material is then separated from the image bearing member. A fixing device applies heat and pressure to the recording material to which the toner is transferred so as to fix the toner on the recording material.
In the image forming apparatus, an intermediate transfer belt system may be employed in transferring the developed image to the recording material by the transfer device. A disadvantage of the intermediate transfer system is that an image defect occurs when a developed image is transferred to a recording material. In particular, an image defect of scattering occurs due to scattering of toner resulting in that a developed image on an intermediate transfer belt cannot be accurately transferred. Japanese Patent Application Laid-Open No. 2003-167444 discusses an invention to reduce such image defects due to scattering of toner.
The invention discussed in Japanese Patent Application Laid-Open No. 2003-167444 relates to an image forming apparatus in which a toner layer is deposited on an intermediate transfer member, and the toner layer is then transferred to a recording material at a secondary transfer portion at one time. In the invention of Japanese Patent Application Laid-Open No. 2003-167444, one of a pair of conveying rollers in the upstream proximity of the secondary transfer portion is set to have higher circumferential speed and greater coefficient of friction against the recording material than the other conveying roller of the pair. The conveying roller having higher circumferential speed and greater coefficient of friction is one which abuts a non-image forming surface of the recording material. With such a structure, an image defect due to abnormal electrical discharge immediately before the secondary transfer portion can be prevented from occurring, and a high quality image can be output.
However, the invention discussed in Japanese Patent Application Laid-Open No. 2003-167444 is disadvantageous in the following respect due to the rigidity of the recording material when the recording material is held by a nip portion of the secondary transfer portion. Specifically, if the recording material has high rigidity, the recording material is shifted toward the intermediate transfer belt side and gets curved when the recording material is held by the nip portion. Then, a gap is generated between the recording material and the intermediate transfer belt within the transfer electric field, and the toner forming the developed image scatters. A defective image is thus formed.
On the contrary, if the recording material has low rigidity, the distance between the recording material and the intermediate transfer belt increases in a transfer region formed in the vicinity of the nip portion when the recording material is held by the nip portion. Then, the toner forming the developed image scatters in the transfer electric field, thus forming a defective image
In view of the circumstances, the present invention provides an image forming apparatus which can reduce load applied to a recording material during secondary transfer to reduce image defects due to scattering of the toner occurring at a secondary transfer portion.
The present invention provides an image forming apparatus which reduces disturbance of a toner image transferred to a recording material at a secondary transfer portion.